Effects of gravity on thermal fluid systems and small living things can be tested.
An improved magnetic levitation apparatus (“Maglev Facility”) has been built for use in experiments in which there are requirements to impose variable gravity (including zero gravity) in order to assess the effects of gravity or the absence thereof on physical and physiological processes. The apparatus is expected to be especially useful for experiments on the effects of gravity on convection, boiling, and heat transfer in fluids and for experiments on mice to gain understanding of bone loss induced in human astronauts by prolonged exposure to reduced gravity in space flight.
The maglev principle employed by the apparatus is well established. The basic equation for equilibrium levitation of a diamagnetic object is
|χB∇zB/μ0| = ρg,
Superconducting Electromagnet generates a static magnetic field with a vertical gradient. For water or other substances of diamagnetism, the gradient magnetic field opposes or aids the gravitational body force by an amount that varies with position along the bore." class="caption" align="left">where χ is the magnetic susceptibility of the object, B is the magnitude of the magnetic-flux density, μ0 is the magnetic permeability of the vacuum, ρ is the mass density of the object, g is the local gravitational acceleration, and ∇zB is the vertical gradient of the magnetic field. Diamagnetic cryogenic fluids such as liquid helium have been magnetically levitated for studying their phase transitions and critical behaviors. Biological entities consist mostly
of diamagnetic molecules (e.g., water molecules) and thus can be levitated by use of sufficiently strong magnetic fields having sufficiently strong vertical gradients.
The heart of the present maglev apparatus is a vertically oriented superconducting solenoid electromagnet (see figure) that generates a static magnetic field of about 16 T with a vertical gradient sufficient for levitation of water in normal Earth gravity. The electromagnet is enclosed in a Dewar flask having a volume of 100 L that contains liquid helium to maintain superconductivity. The Dewar flask features a 66-mm-diameter warm bore, lying within the bore of the magnet, wherein experiments can be performed at room temperature. The warm bore is accessible from its top and bottom ends. The superconducting electromagnet is run in the persistent mode, in which the supercurrent and the magnetic field can be maintained for weeks with little decay, making this apparatus extremely cost and energy efficient to operate. In addition to water, this apparatus can levitate several common fluids: liquid hydrogen, liquid oxygen, methane, ammonia, sodium, and lithium, all of which are useful, variously, as rocket fuels or as working fluids for heat transfer devices. A drop of water 45 mm in diameter and a small laboratory mouse have been levitated in this apparatus.
This work was done by Yuanming Liu, Donald M. Strayer, and Ulf E. Israelsson of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category. NPO-45886
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